I love redstone and the endless possibilities for creation.

I normally use them for trap doors, since sticky pistons can be used to slide stone. I'll keep the lever on the surface and I leave no tell-tale signs of redstone anywhere. 

I also use them to make sliding doorways for houses and mob killing. With activator rails I've made mechanisms work on a timed delay. 

I haven't experimented with creating calculators, but the fact that they've been created really show me how much potential redstone devices have.

What about you, what redstone devices do you make?

EideticMemory : I like to do repeater stuff.

I like creating a machine gun or something. I one time made a automatic sugarcane farm. I tried making a cactus version but I failed hard. A automatic wheat farm is easy but try making a cactus one and you'll see the difficulty with that.

I am really bad at redstone. I watch all of thease people make amazing things like Highscore tables and elevators when I am stuck at the basics. 
Most of my redstone stuff is just roller coasters but they are based of design more than anything and there is little redstone dust required.

My most techniqual red stone piece is a secret door I made in this castle with an alarm from a trip wire inside if you went in incorrectly.

MechaMento : That has been the same way with me, I haven't been really that advance with the redstone than some people I seen on YouTube, the most I did was using the redstone to turn all the lamps in my house on and off and also using it as a lockdown door against hostile mobs, other than that, that's mostly it.

I really don't use much red stone, and I can't build with it at all. I normally just stick with the normal roller coaster and things. It is kind of sad when I see these people make giant structures out of it.

hunter31626 : Automatic cactus farms are easy to make, but are kinda pointless unless you play on a faction server. (they let you sell items in a shop)
Just plant a cactus in the air and put a block above it. When the cactus will grow it will be dropped to the bottom. On the bottom put water flowing into the middle and in the middle place a hopper leading into a chest.
There is no redstone needed.

I've made automatic wheat farms and mob grinders before. Nothing too fancy.
When I get time I plan on making an automatic cocoa bean farm to make cookies. Cookies sell for a lot on the faction server I play on. Maybe i'll make a snow farm or pumpkin/ melon farm too.

The only two redstone mechanisms i really know how to make are clocks and NOT gates. I use NOT gates to power my house and clocks when i'm on a server to hook it up to a command block. The command blocks orders are to tp a player to the same area with every tick. Good fun.

I am terrible with redstone, so I can only build the basic contraptions like the piston door or the lockgates for a dock. I am attempting to build my redstone weapon arsenal with a Fully Automatic Dispenser and it is working.

I love creating power rails.....using redstone. Well because i be making roller coasters with them or i random make the rails go to random places and back to my house. (Minecarts are awesome :3)

In spite of the staggering amount of time I spend playing this game, I actually use very little redstone.? What I do build with it is simple hidden doors, trap doors, and other similar items.? The few times that I've tried using redstone to create something of any scale, its turned into a source of frustration (Like the castle gates I'm currently trying to build in one of my worlds.)? I kind of wish I was able to stumble across a good how-to guide for redstone, . . .

I expect that at some point, I will have a "eureka!" moment and I will suddenly grasp the multilayer concept for activating a series of blocks at the same time, or in the sequence I desire, but for now, activating one, maybe two blocks at a time is the extent of my redstone use.

The only thing I make extensive use of redstone for is powered rails it seems.

*EDIT*  I just remembered another thing I sometimes make with Redstone.  I will sometimes put a piston on the floor with a redstone torch underneath it in order to create a table.